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Wind shear detection using the Next Generation Airport Surveillance Radar

July 12, 1999
  |
Project Report
Author:
Mark E. Weber
Published in:
MIT Lincoln Laboratory Report ATC-266
Topic:
algorithms
R&D area:
R&D group:

Summary

The Federal Aviation Administration (FAA) is deploying a Weather Systems Processor (WSP) for the current-generation Airport Surveillance Radar - ASR-9. This modification exploits the coherency of the ASR-9 to perform Doppler wind measurement. Signature recognition algorithms then automatically detect low altitude wind shear phenomena, track thunderstorm motion and display appropriate graphical and alphanumeric alerts to air traffic control (ATC) personnel. The FAA and U.S. Air Force are now procuring an ASR-11 to replace older terminal surveillance radars at facilities that did not receive the ASR-9. Although the antenna pattern, scan rate and energy-on-target of the ASR-11 match the corresponding parameters of the ASR-9, two other characteristics are markedly different. It utilizes a low peak power solid state transmitter that requires transmission of long, coded waveforms and a pulse compression receiver. Secondly, its pulse transmission sequence consists of short (five-pulse) bursts at both different pulse-repetition frequencies (PRF) and different RF frequencies. In this report, we assess the technical and operational issues associated with adding a WSP to the ASR-11. The existing WSP data processing and display technology are largely re-usable for the ASR-11 based WSP. Ground clutter filter coefficients and the length and number of coherent processing intervals would need to be changed to conform to the ASR-11 pulse transmission strategy, and straightforward adaptations to the equations used in the pulse-pair weather reflectivity and Doppler velocity estimation would be required. With these changes, the ASR-11 could host the WSP, subject to performance degradations for low reflectivity wind shear phenomena such as dry microbursts and gust fronts. A benefits assessment waas performed to evaluate the operational requirements for an ASR-11 based WSP. Given that the FAA has already committed to deploy improved Low Level Wind Shear Alert Systems (LLWAS) at most ASR-11 airports, the incremental safety benefits for the ASR-11 WSP appear to be less than the cost of the equipment. A case can be made for deployment based on "situational awareness" benefits that the WSP has been demonstrated to provide to air traffic controllers. We estimate that the value to the public and airline industry of reductions in aircraft delay, and avoidance of unnecessary diversions, would be in excess of eight million dollars per year tallied across 18 of the larger ASR-11 equipped airports.
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Summary

The Federal Aviation Administration (FAA) is deploying a Weather Systems Processor (WSP) for the current-generation Airport Surveillance Radar - ASR-9. This modification exploits the coherency of the ASR-9 to perform Doppler wind measurement. Signature recognition algorithms then automatically detect low altitude wind shear phenomena, track thunderstorm motion and display appropriate...

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Wind shear detection using the Next Generation Airport Surveillance Radar

The behavior of total lightning activity in severe Florida thunderstorms

July 1, 1999
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Journal Article
Author:
Earle R. Williams
…
Published in:
Atmos. Res., Vol. 51, Nos. 3-4, July 1999, pp. 245-265.
Topic:
weather
R&D area:
R&D group:

Summary

The development of a new observational system called LISDAD (Lightning Imaging Sensor Demonstration and Display) has enabled a study of severe weather in central Florida. The total flash rates for storms verified to be severe are found to exceed 60 fpm, with some values reaching 500 fpm. Similar to earlier results for thunderstorm microbursts, the peak flash rate preceeds the severe weather at the ground by 5-20 min. A distinguishing feature of severe storms is the presence of lightning 'jumps' -- abrupt increases in flash rate in advance of the maximum rate for the storm. The systematic total lightning precursor to severe weather of all kinds -- wind, hail, tornadoes -- is interpreted in terms of the updraft that sows the seeds aloft for severe weather at the surface and simultaneously stimulates the ice microphysics that drives the intracloud lightning activity.
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Summary

The development of a new observational system called LISDAD (Lightning Imaging Sensor Demonstration and Display) has enabled a study of severe weather in central Florida. The total flash rates for storms verified to be severe are found to exceed 60 fpm, with some values reaching 500 fpm. Similar to earlier...

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The behavior of total lightning activity in severe Florida thunderstorms

Understanding-based translingual information retrieval

June 17, 1999
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Conference Paper
Author:
Young-Suk Lee
…
Published in:
4th Int. Conf. on Applications of Natural Language to Information Systems, 17-19 June 1999, pp. 187-195.
Topic:
machine translation
R&D area:
R&D group:

Summary

This paper describes our preliminary research on an understanding-based translingual information retrieval system for which the input to the system is a query sentence in English, and the output of the system is a set of documents either in English or in Korean. The understanding module produces a meaning representation --- called semantic frame --- of the input sentence where the predicate-argument structure and the question-type of the input are identified, and each keyword is assigned its concept category. The translingual search module performs search on an English and Korean bilingual corpus tagged with concept categories. The results of our preliminary experiment, performed an a document set consisting of slides and notes from English and Korean briefings in a military domain, indicate that an understanding-based approach to information retrieval combined with concept-based search technique improves both precision and recall compared with a keyword match technique without understanding for both monolingual- and translingual retrieval. Current work is directed at further development of the system, and in preparation for tests on larger copora.
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Summary

This paper describes our preliminary research on an understanding-based translingual information retrieval system for which the input to the system is a query sentence in English, and the output of the system is a set of documents either in English or in Korean. The understanding module produces a meaning representation...

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Understanding-based translingual information retrieval

Demonstration of a 630-GHz photomixer used as a local oscillator

June 13, 1999
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Conference Paper
Author:
Erik K. Duerr
…
Published in:
1999 IEEE MTT-S Int. Microwave Symp. Digest, Vol. 1, 13-19 June 1999, pp. 127-130.
Topic:
lasers
R&D area:
R&D group:

Summary

We report the first successful demonstration of a photomixer local oscillator (LO) integrated with a superconducting heterodyne detector. The photomixer LO generated the difference frequency of two diode lasers by optical heterodyne conversion in low-temperature-grown GaAs. The measured receiver noise temperature, 331 K at 630 GHz, compares favorably with that achieved using a varactor-multiplier LO. We also report the design of a high-power distributed photomixer structure.
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Summary

We report the first successful demonstration of a photomixer local oscillator (LO) integrated with a superconducting heterodyne detector. The photomixer LO generated the difference frequency of two diode lasers by optical heterodyne conversion in low-temperature-grown GaAs. The measured receiver noise temperature, 331 K at 630 GHz, compares favorably with that...

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Demonstration of a 630-GHz photomixer used as a local oscillator

Comparisons of long-term Schumann resonance records in Europe and North America

June 7, 1999
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Conference Paper
Author:
G. Satori
…
Published in:
11th Int. Conf. on Atmos. Electr. 7-11 June 1999, pp. 705-708.
Topic:
electrical engineering
R&D area:
R&D group:

Summary

Two stations at a distance comparable with the wavelength in the Schumann resonance (SR) frequency range, one in Europe (Nagycenk, Hungary) and one in North America (West Greenwich, Rhode Island) have simultaneously monitored the natural vertical electric and horizontal magnetic field components in the frequency range of 3-25 Hz. This is a unique opportunity, as Schumann resonance stations are scarce and even fewer station have records with 5-6 year durations. The main purpose of this paper is to make comparisons in the SR time series measured simultaneously at the two field sites, thereby providing access to global behavior on the seasonal and interannual time scales. The comparative measurements described here point out distinct differences in the nature of convection in South America and in Africa, and reveal new aspects about the behavior of tropical continental convection on the ENS0 time scale.
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Summary

Two stations at a distance comparable with the wavelength in the Schumann resonance (SR) frequency range, one in Europe (Nagycenk, Hungary) and one in North America (West Greenwich, Rhode Island) have simultaneously monitored the natural vertical electric and horizontal magnetic field components in the frequency range of 3-25 Hz. This...

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Comparisons of long-term Schumann resonance records in Europe and North America

Schumann Resonances and the temporal-spatial dynamics of global thunderstorm activity

June 7, 1999
  |
Conference Paper
Author:
V. Mushtak
…
Published in:
11th Int. Conf. on Atmospheric Electricity, 7-11 June 1999, pp. 698-700.
Topic:
weather
R&D area:
R&D group:

Summary

A two-dimensional computational ELF technique has been applied to interpret variations of peak frequencies of Schumann resosnances (SR) observed at the MIT experimental site (West Greenwich, Rhode Island). The spatial-temporal dynamics of global thunderstorm activity has been simulated on the basis of general meteorological data. It is shown that the proposed models provide a reasonable qualitative agreement between computed and observed variations for SR I to IV. Some inverse task diagrams has been constructed as an instrument for distinguishing between day-to-day thunderstorm scenarios.
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Summary

A two-dimensional computational ELF technique has been applied to interpret variations of peak frequencies of Schumann resosnances (SR) observed at the MIT experimental site (West Greenwich, Rhode Island). The spatial-temporal dynamics of global thunderstorm activity has been simulated on the basis of general meteorological data. It is shown that the...

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Schumann Resonances and the temporal-spatial dynamics of global thunderstorm activity

The relationship between the background and transient signals in Schumann resonances

June 7, 1999
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Conference Paper
Author:
Earle R. Williams
…
Published in:
Proc. 11th Int. Conf. on Atmospheric Electricity, 7-11 June 1999, pp. 758-761.
Topic:
weather
R&D area:
R&D group:

Summary

Two distinct measures of the Earth's Schumann resonances -- the background and the transients -- are studied through comparisons at the mesoscale and at the continental scale. A rough proportionality is shown between the far more abundant afternoon lightning activity and the larger positive mesoscale discharges that make sprites and simultaneously ring the Earth- ionosphere cavity to levels higher than the integration of all other lightnings.
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Summary

Two distinct measures of the Earth's Schumann resonances -- the background and the transients -- are studied through comparisons at the mesoscale and at the continental scale. A rough proportionality is shown between the far more abundant afternoon lightning activity and the larger positive mesoscale discharges that make sprites and...

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The relationship between the background and transient signals in Schumann resonances

Total lightning activity associated with tornadic storms

June 7, 1999
  |
Conference Paper
Author:
Steven J. Goodman
…
Published in:
11th Int. Conf. on Atmos. Electr., 7-11 June 1999, pp. 515-518.
Topic:
weather
R&D area:
R&D group:

Summary

Severe storms often have high flash rates (in excess of one flash per second) and are dominated by intracloud lightning activity. In addition to the extraordinary flash rates, there is a second distinguishing lightning characteristic of severe storms that seems to be important. When the total lightning history is examined, one finds sudden increases in the lightning rate, which we refer to as lightning "jumps", that precede the occurrence of severe weather by ten or more minutes. These jumps are typically 30-60 flashes/min, and are easily identified as anomalously large derivatives in the flash rate. This relationship is associated with updraft intensification and updraft strength is an important factor in storm severity (through the accumulation of condensate aloft and the stretching of vorticity). In several cases, evidence for diminishment of midlevel rotation and the descent of angular momentum from aloft is present prior to the appearance of the surface tornado. Based on our experience with severe and tornadic storms in Central Florida, we believe the total lightning may augment the more traditional use of NEXRAD radars and storm spotters. However, a more rigorous relation of these jumps to storm kinematics is needed if we are to apply total lightning in a decision tree that leads to improved warning lead times and decreased false alarm rates.
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Summary

Severe storms often have high flash rates (in excess of one flash per second) and are dominated by intracloud lightning activity. In addition to the extraordinary flash rates, there is a second distinguishing lightning characteristic of severe storms that seems to be important. When the total lightning history is examined...

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Total lightning activity associated with tornadic storms

Security implications of adaptive multimedia distribution

June 6, 1999
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Conference Paper
Author:
Thomas M. Parks
…
Published in:
Proc. IEEE Int. Conf. on Communications, Multimedia and Wireless, Vol. 3, 6-10 June 1999, pp. 1563-1567.
Topic:
communications
R&D area:
R&D group:

Summary

We discuss the security implications of different techniques used in adaptive audio and video distribution. Several sources of variability in the network make it necessary for applications to adapt. Ideally, each receiver should receive media quality commensurate with the capacity of the path leading to it from each sender. Several different techniques have been proposed to provide such adaptation. We discuss the implications of each technique for confidentiality, authentication, integrity, and anonymity. By coincidence, the techniques with better performance also have better security properties.
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Summary

We discuss the security implications of different techniques used in adaptive audio and video distribution. Several sources of variability in the network make it necessary for applications to adapt. Ideally, each receiver should receive media quality commensurate with the capacity of the path leading to it from each sender. Several...

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Security implications of adaptive multimedia distribution

Rotating a weather map

June 1, 1999
  |
Journal Article
Author:
Robert D. Grappel
Published in:
Dr. Dobb's J., Vol. 24, No. 6, June 1999, pp. 80-88.
Topic:
aircraft
R&D area:
R&D group:

Summary

Introduction: I was recently part of a project developing a system for aircraft pilots to access the national ground weather-radar database while in flight. This weather-radar graphical database is generated from the outputs of the FAA and National Weather Service network of radars covering the continental United States and is updated every five minutes. Each pixel in the database covers a square measuring two kilometers (about one nautical mile) on a side. The content of each data pixel is a measure of the radar reflectivity measured at that location - radar reflectivity is proportional to the water content in the atmosphere (the precipitation rate). This graphical database is available through several commercial vendors - it's what you see displayed on The Weather Channel or during typical TV weather reports. Our system, on the other hand, provides a low-speed digital datalink connection from an FAA ground computer to an avionics computer/display located in the aircraft cockpit.
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Summary

Introduction: I was recently part of a project developing a system for aircraft pilots to access the national ground weather-radar database while in flight. This weather-radar graphical database is generated from the outputs of the FAA and National Weather Service network of radars covering the continental United States and is...

READ MORE
Rotating a weather map
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